Terminology

Equivalent names for the same thing

• linear model
• linear regression
• linear regression model

Different kinds of linear regression models

Term	Definition
Simple regression	Linear regression with one predictor
Multiple regression	Linear regression with more than one predictor

Data and variable types

Term	Definition
Observation, observational unit	The individual entities on which data are collected (often the rows in a data frame)
Variable	Any characteristic recorded on the observational units (often the columns in a data frame)
Numeric variable	A variable that records a numeric quantity for each case. For such variables standard arithmetic operations make sense. For example: height, IQ, and weight
Categorical variable	A categorical variable places units into one of several groups. For example: country of birth, dominant hand, eye colour
Binary variable	A special case of categorical variable with only two possible levels. For example: dominant hand (left or right), smoking status (smoker or non-smoker), answered question correctly (yes or no)
Outcome variable, dependent variable (DV), response variable	Variable which measures the outcome of interest in a study
Predictor, independent variable (IV), explanatory variable	Variable which is used to explain differences/changes in the response variable

Study designs

Term	Definition
Observational study	An observational study is a study in which the researcher does not manipulate any of the variables involved in the study, but merely records the values as they naturally exist
Experimental study	An experiment is a study in which the researcher imposes the values of the explanatory variable on the units before measuring the response variable